1. Field of the Invention
The present invention is related to a device which compresses a still image data in accordance with a JPEG (Joint Photographic Expert Group) algorithm and records the compressed image data in a recording medium and, also, to a device which reads the compressed image data from the recording medium and expands the compressed image data to reproduce the still image.
2. Description of the Related Art
A standard algorithm, for the encoding of high resolution images and the transfer of that information through telecommunication transmission channels, has been recommended by the JPEG. In order to enable a large-scale data compression, the baseline process of the JPEG algorithm breaks down the original image data into components on a spatial frequency axis using a two-dimensional DCT process. Thereafter, the data expressed on the spatial frequency axis is quantized by using a quantization table. The quantized data is then encoded using a Huffman table.
The encoded (or compressed) image data can be expanded by carrying out a process, which is the inverse of the compression process described above, so that the original image data can be reproduced. Namely, the compressed image data is decoded, is subjected to a dequantization process, using a quantization table, and is, finally, subjected to a two dimensional inverse discrete transformation, so that the original image data is reproduced.
For example, there are two methods to obtain a mosaic-processed image. Note that a mosaic-process means that a luminance data Y and color difference data Cb and Cr, corresponding to each pixel included in one block forming a part of one frame image, are set to identical data values, respectively, by averaging the data for one block. A first method is that an original image, which has been subjected to the mosaic-process, is compressed and recorded in a recording medium, and then, the compressed image data is subjected to an expansion process. Thus, the mosaic-processed image is reproduced. In a second method, an original image, which has not been subjected to a mosaic-process, is compressed and recorded in a recording medium. Then, this compressed image data is subjected to an expansion process and is, finally, mosaic-processed, so that the mosaic-processed image is reproduced.
According to the first method, however, an image which is not mosaic-processed cannot be reproduced, since the original image has been mosaic-processed. Conversely, the second method should be provided with a step for performing the mosaic-process.